Date   : Wed, 01 Oct 2003 00:18:07 +0100 
From   : Andrew Hancock <Andrew.Hancock@...>
Subject: Re: BBC Micro lazy delayed boot!

I've also looked at Pin 8 NMI (bar) IC77

I thought this gave an interesting result, but could be normal.

At power-on (when the first beep is produced) this is high and low with
pulses > 10Hz, for a short period.

And then, high with pulses of low > 30ns for 15 seconds and then reverts to 

Beeb has booted successfully this is high and low with pulses > 10Hz.

> -----Original Message-----
> From: Andrew Hancock [mailto:Andrew.Hancock@...]
> Sent: 30 September 2003 23:57
> To: 'bbc-micro@...'
> Subject: RE: [BBC-Micro] BBC Micro lazy delayed boot!
> 
> Thanks to Pete Turnbull on this list I've got a logic probe. So I can
> start
> probing around the motherboard having a look at various logic states.
> 
> With 8271 chip installed.
> 
> So far, many contributors have stated check
> 
> 1. Outputs of IC 16
> 
> IC 16 555 Output
> 
> Pin 3 (input to IC 33) RST Transitions from high to low very quickly.
> Stays LOW
> 
> IC 33 74LS04
> 
> Pin 3 Transitions from high to low very quickly.
> Pin 4 (output) (bar) RST Transitions from low to high very quickly. Stays
> HIGH.
> 
> IC 1 6502
> 
> Pin 4 High to Low at power-on, then High with pulses of low > 30ns
> Pin 6 NMI PERMANENTLY HIGH. No transition observed.
> 
> 
> 
> WITHOUT 8271 installed.
> 
> As above.
> 
> Except IC 1 6502
> 
> Pin 6 NMI PERMANENTLY LOW No transition observed.
> 
> I'm not too sure if I've mentioned this previously but with the 8271 chip
> installed, the 15 second delay only occurs, when the DNFS 1.2 rom is
> installed.
> 
> So it's a combination of both 8271 & DNFS 1.2 rom, that causes the delay.
> 
> Any ideas, where else should I stick my logic probe!
> 
> Regards
> 
> Andrew
> 
> PS it's also hard work reading the motherboard circuit diagram on an A4
> sheet!
> 
> > -----Original Message-----
> > From: Sprow [mailto:info@...]
> > Sent: 28 September 2003 19:46
> > To: 'bbc-micro@...'
> > Subject: Re: [BBC-Micro] BBC Micro lazy delayed boot!
> >
> > In article
> > <6A4F555CEA3CD5118DBD0002E30AC0912C0838@...>,
> >    Andrew Hancock <Andrew.Hancock@...> wrote:
> >
> > [snip]
> >
> > > The problem still exist, I think I'll have to start checking logic
> > states
> > > nNMI and nIRQ lines on the CPU with a logic probe and output of IC16
> and
> > > IC33,giving the huge ceramic disc capacitor a wiggle as Sprow
> suggested.
> > >
> > > Which huge ceramic disc capacitor?
> >
> > The one just next to IC16 (a 555).There are two actually,but only one
> > governs the reset pulse width.
> >
> > > And how do I proceed with checking checking logic states nNMI and nIRQ
> > > lines on the CPU with a logic probe and output of IC16 and IC33?
> > >
> > > Apart from first I'll have to purchase a logic probe!
> >
> > Just an LED connected via a spare gate will do,or looking on a scope set
> > to
> > 1V/cm vertical.
> >
> > I'm a little puzzled how DFS 0.90 and DFS 1.20 are
> different,particularly
> > if
> > there's no NFS chip fitted,as NFS also has an intimate relationship with
> > nNMI,
> > Sprow.